PCA EB234 Guide to Full-Depth Reclamation (FDR) With Cement

Guide to Full-DepthReclamation (FDR)

with CementBy David R. Luhr, Wayne S. Adaska, Gregory E. Halsted

Guide to Full-DepthReclamation (FDR)with Cement

Portland Cement Association5420 Old Orchard RoadSkokie, Illinois 60077-1083847.966.6200 Fax 847.966.9781www.cement.org

Guide to Full-Depth Reclamation (FDR) with Cement

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Abstract: Full-depth reclamation (FDR) is a roadway rehabilitation process that recycles the materials fromdeteriorated asphalt pavement, and, with the addition of portland cement, creates a new stabilized base.This guide to FDR discusses its applications, benefits, design, construction, and testing.

Keywords: Full-depth reclamation, FDR, flexible pavement, base failure, pavement structure, pavementdesign, field evaluation, moisture/density relationship, mix design, Tube Suction Test, construction process,reflective cracking, soil-cement, cement-treated base, CTB, cement-treated soil.

Reference: Luhr, David, R.; Adaska, Wayne, S.; Halsted, Gregory, E., Guide to Full-Depth Reclamation withCement, EB234 Portland Cement Association, Skokie, Illinois, USA, 2005, 14 pages.

About the Authors: David R. Luhr, PhD, P.E., Program Manager, Portland Cement Association, Post OfficeBox 5895, Cary, North Carolina 27511, USA.

Wayne S. Adaska, P.E., Director of Public Works, Portland Cement Association, 5420 Old Orchard Road,Skokie, Illinois 60077-1083, USA.

Gregory E. Halsted, P.E., Pavements Engineer, Portland Cement Association, Post Office Box 5113,Bellingham, Washington 98227-5113, USA.

Print HistoryFirst Printing 2005

©2005, Portland Cement Association

All rights reserved. No part of this book may be reproduced in any form without permission in writing fromthe publisher, except by a reviewer who wishes to quote brief passages in a review written for inclusion in amagazine or newspaper.

Portland Cement Association (“PCA”) is a not-for-profit organization and provides this publicationsolely for the continuing education of qualified professionals. THIS PUBLICATION SHOULD ONLY BEUSED BY QUALIFIED PROFESSIONALS who possess all required license(s), who are competent to eval-uate the significance and limitations of the information provided herein, and who accept total respon-sibility for the application of this information. OTHER READERS SHOULD OBTAIN ASSISTANCE FROM AQUALIFIED PROFESSIONAL BEFORE PROCEEDING.

PCA AND ITS MEMBERS MAKE NO EXPRESS OR IMPLIED WARRANTY WITH RESPECT TO THIS PUBLI-CATION OR ANY INFORMATION CONTAINED HEREIN. IN PARTICULAR, NO WARRANTY IS MADE OFMERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. PCA AND ITS MEMBERS DISCLAIMANY PRODUCT LIABILITY (INCLUDING WITHOUT LIMITATION ANY STRICT LIABILITY IN TORT) INCONNECTION WITH THIS PUBLICATION OR ANY INFORMATION CONTAINED HEREIN.

ISBN 0-89312-247-5

EB234

WARNING: Contact with wet (unhardened) concrete, mortar, cement, or cement mixtures can causeSKIN IRRITATION, SEVERE CHEMICAL BURNS (THIRD DEGREE), or SERIOUS EYE DAMAGE. Frequentexposure may be associated with irritant and/or allergic contact dermatitis. Wear waterproof gloves,a long-sleeved shirt, full-length trousers, and proper eye protection when working with these mate-rials. If you have to stand in wet concrete, use waterproof boots that are high enough to keep con-crete from flowing into them. Wash wet concrete, mortar, cement, or cement mixtures from yourskin immediately. Flush eyes with clean water immediately after contact. Indirect contact throughclothing can be as serious as direct contact, so promptly rinse out wet concrete, mortar, cement, orcement mixtures from clothing. Seek immediate medical attention if you have persistent or severediscomfort.

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Table of Contents1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Determining When FDR is Appropriate ………………………… . . . . . . . . . . . . . . . . . . . . 2

Serious Damage or Base Failure ………………………………… . . . . . . . . . . . . . . . . . . . . 2

Excessive Patching ……………………………………………….. . . . . . . . . . . . . . . . . . . . . 2

Inadequate Pavement Structure ………………………………….. . . . . . . . . . . . . . . . . . . . 2

Special Considerations When Using FDR ………………………. . . . . . . . . . . . . . . . . . . . . 3

2 Design ………………………………………………………………... . . . . . . . . . . . . . . . . . . 4

Performing the Initial Field Evaluation …………………………………. . . . . . . . . . . . . . . . 4

Pavement Design ………………………………………………….. . . . . . . . . . . . . . . . . . . . 4

Mix Design ………………………………………………………... . . . . . . . . . . . . . . . . . . . . 5

Balanced Design …………………………………………………... . . . . . . . . . . . . . . . . . . . 6

Aggregate Adjustment ……………………………………………. . . . . . . . . . . . . . . . . . . . 6

Moisture Sensitivity ………………………………………………. . . . . . . . . . . . . . . . . . . . . 6

3 Construction ………………………………………………………….. . . . . . . . . . . . . . . . . . 8

Pulverizing ………………………………………………………... . . . . . . . . . . . . . . . . . . . . 8

Grading, Shaping, and Widening …………………………………. . . . . . . . . . . . . . . . . . . 8

Cement Placement ………………………………………………... . . . . . . . . . . . . . . . . . . . 9

Mixing …………………………………………………………….. . . . . . . . . . . . . . . . . . . . 10

Compaction and Final Grading ……………………………………. . . . . . . . . . . . . . . . . . 10

Curing …………………………………………………………….. . . . . . . . . . . . . . . . . . . . 10

Surfacing ………………………………………………………….. . . . . . . . . . . . . . . . . . . . 10

Field Quality Control ……………………………………………... . . . . . . . . . . . . . . . . . . . 10

Traffic Control ……………………………………………………. . . . . . . . . . . . . . . . . . . . 10

Reflective Cracking ………………………………………………. . . . . . . . . . . . . . . . . . . . 11

4 Suggested Construction Specification for Full-Depth Reclamation … . . . . . . . . . . . 12


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1

1 Introduction

When asphalt pavements fail, determining the best rehabili-tation procedure can be difficult. A simple asphalt overlay ora “mill and fill” approach can improve the appearance of thepavement surface, but may do little to correct the underlyingproblems that caused the failure in the first place. Within ashort period of time the problems will likely reappear.

Long-term solutions to failed asphalt pavements include athick structural overlay or complete removal and replacement

of the existing base and asphalt surface. Both methods canbe very expensive and wasteful of virgin aggregates.

A third choice, recycling the failed asphalt pavement througha process called “full-depth reclamation” (FDR) usingportland cement, can provide the benefits of reconstructionwithout the substantial costs and environmental concerns.This procedure pulverizes the existing asphalt and blends itwith underlying base, subbase, and/or subgrade materials,

Table 1 - Characteristics of Flexible Pavement Rehabilitation Strategies

Solution Advantages Disadvantages

Thick • Provides new pavement structure • Elevation change can present problems for existing Structural • Quick construction curb & gutter and overhead clearancesOverlay • Only moderate traffic disruption • Large quantity of material must be imported

• Old base/subgrade may still need improvement• High cost alternative

Removal and • Provides new pavement structure • Long construction cycle requiring detours andReplacement • Failed base and subgrade are eliminated inconvenience to local residents/businesses

• Existing road profile/elevation • Increased traffic congestion due to detours, can be maintained construction traffic

• Rain or snow can significantly postpone completion• Large quantity of material must be imported• Old materials must be dumped• Highest cost alternative

Recycling • Provides new pavement structure • May require additional effort to correct Surface, Base • Fast construction cycle subgrade problemsand Subgrade • No detours • Some shrinkage cracks may reflect through with Cement • Minimal change in elevation, thus eliminating bituminous surface(Full-Depth problems with curb/gutter, overhead clearancesReclamation) • Minimal material transported in or out

• Conserves resources by recycling existing materials

• Local traffic returns quickly• Rain does not affect construction

schedules significantly• Provides moisture- and frost-resistant base• Least cost alternative


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which are mixed with cement and compacted to provide anew stabilized base. A new surface is then applied, whichcompletes the FDR process, providing a new roadway struc-ture using recycled materials from the failed pavement.Because of cement stabilization, the new base will be moreuniform, stronger, and provide better long-term performancethan the original pavement.

The cost advantages of recycling materials from the originalpavement are obvious; however, there are other environmentaladvantages that are important to the FDR process:

• Conservation of new aggregates that must be quarriedand transported to the site

• Conservation of land areas that would be used to dispose of the asphalt and base materials from the failed pavement

• Reduced air pollution, traffic congestion, and damage ofnearby roadways resulting from hauling new materials tothe site, and disposal of old materials

This document provides an overview of the FDR processusing cement, making reference to additional documents ineach section if more information is desired.

Determining When FDR Is Appropriate

FDR is most appropriate under the following conditions:

• The pavement is seriously damaged and cannot be reha-bilitated with simple resurfacing.

• The existing pavement distress indicates that the problemlikely exists in the base or subgrade.

• The existing pavement distress requires full-depthpatching over more than 15%-20% of the surface area.

• The pavement structure is inadequate for the current orfuture traffic.

Serious Damage or Base Failure

An engineer can evaluate the reasons for pavement failureby observing the types of distress that are visible. Forexample, alligator cracking, deep depressions, or soil stainson the surface are all signs of base or subgrade problems inthe pavement structure (Figure 1.1).

Excessive Patching

Although patching is often necessary to keep a road service-able, it can be expensive. In fact, once the area of full-depthpatching exceeds 15%-20%, simple math proves it lessexpensive to use FDR than to perform the patching. Ofcourse, the final product achieved with FDR is far superior toa road that is severely patched. Figure 1.2 is an example of aheavily patched pavement that was selected for FDR.

Inadequate Pavement Structure

Often the traffic patterns on a road will change over theyears. This sometimes results in roads that were originally

Figure 1.1 Example of pavement distress indicating base problems.

Figure 1.2 Excessive patching is often more expensive than FDR.

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FDR, where the pavement can be strength-ened by “building the pavement down”(Figure 1.3). By reclaiming the existing pave-ment into a stabilized base, the road isstrengthened without the requirement ofmore right-of-way.

Special Considerations WhenUsing FDR

Because the pulverized asphalt from theexisting pavement (called “reclaimed asphaltpavement,” or RAP) is blended with theunderlying base materials, the thickness ofreclaimed asphalt cannot exceed the depthof reclamation for an extended length (shortsections of full-depth asphalt, like a patch,are allowed). If a long section of thickasphalt is selected for reclamation, theasphalt layer can be partially milled and the RAP stockpiled for future use. Theremaining asphalt in the old pavement is

then reclaimed and blended with the base.

Another consideration when evaluating FDR is the existenceof large rocks (larger than 4 inches (100 mm) in diameter) inthe base or subgrade. If this material is within the depth ofreclamation, the costs of reclaiming may be high because thecontractor must take into consideration the slower and moredifficult construction that is posed by the rocks.

Chapter 1 Introduction

constructed for light traffic but are now significantly under-designed for existing and future traffic loads. When thishappens, often a road is “built-up” by increasing the thick-ness of the existing pavement structure. However, increasingthe pavement thickness also requires building up andextending the shoulders, since a reasonable shoulder slopeneeds to be maintained for safety. This can requiresignificantly more right-of-way. An alternative exists with

Figure 1.3 Using FDR to “build the pavement down.”

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2 Design

Performing the Initial Field Evaluation

After a road is selected as a candidate for FDR, a field evalua-tion should be performed to determine what materials makeup the current pavement structure. The principal reason forthe field evaluation is to determine: 1) the thickness of thepavement layers, and 2) the materials in each layer that will be blended for the reclaimed base.

In many cases, little will be known about the materials in theexisting pavement and the thickness of the existing layers. Thebest way to determine these will be to sample the roadway.How frequently the samples should be taken depends on howvariable the existing pavement is. Normally if a road is sampledevery 1/4 mile (0.4 km) it will provide adequate information.Sampling can usually be accomplished using a coring rig or ajackhammer for the asphalt and an auger or post-hole diggerfor the base and subgrade.

At each location the thickness of the asphalt layer should be determined. If a core is taken it can be visually examined to see the condition of the asphalt and the size of the aggregate. Digging below the asphalt with an auger or post-hole digger will allow sampling of the base and subgradematerials. The thickness of the base layer and the type ofaggregate should be noted. Also, the depth to subgrade andtype of subgrade material should be recorded.

From a representative location, a sample of road materialsshould be taken back to the laboratory to perform a mixdesign. If the materials are relatively consistent along theproject, only one location needs to be used to collect the labo-ratory sample. If a significant difference occurs in the materialsalong the project, then a second mix design may be necessary.

The easiest way to obtain a laboratory sample is to dig a small“test pit.” For example, a 1 x 1 x 1 -foot (300 x 300 x 300

mm) excavation will provide the materials necessary for themix design, and when exposed will provide a good “picture”of what the individual layers look like. Normally about 100lbs. (45 kg) of material is sufficient (this can be carried in two5-gallon (19-liter) buckets). It is advantageous if the asphalt,base, and subgrade materials can be kept separate, allowingfor different blending ratios in the lab. For example, if theexisting pavement is 3 inches (75 mm) of asphalt and 3 inches(75 mm) of base, in the laboratory it would be possible tomake a 50:50 blend of asphalt and base (for a 6-inch (150 mm) stabilized base), or a 33:33:33 blend of asphalt,base, and subgrade (for a 9-inch (225 mm) stabilized base).This is discussed further in the section on Mix Design.

During the field evaluation is an excellent time to note drainageproblems, locations where culverts or utility crossings arerequired, any recommendations to change grade or cross-slope,or locations where widening is desired. Since the roadway willbe reconstructed from the base up, it is the best time to makedesired permanent changes.

Pavement Design

The thickness design for a reclaimed pavement is similar to thatfor a new pavement structure, since the pavement is beingrebuilt from the subgrade up. In most design procedures an engi-neer has the option of selecting a “cement-treated base” (CTB)for the pavement structure. A reclaimed pavement is designedthe same way, characterizing the reclaimed base as CTB. TheAASHTO procedure for pavement design, for example, uses aStructural Layer Coefficient to model base materials. The PCAthickness design procedure can also be used (PCA publicationThickness Design for Soil-Cement Pavements, EB068).

The new cement-stabilized base from the FDR process willnormally be between 6 inches (150 mm) and 12 inches

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Chapter 2 Design

(300 mm) in depth. Any depth of reclaimed base that ismore than 12 inches (300 mm) will be difficult to compactin one lift and is not recommended.

The ability of a pavement base to carry loads depends on the strength of the base material and the depth of the baselayer. A thin, but strong base can theoretically carry thesame load as a thick, but weaker base. However, the thin,strong base should be avoided because it can becomebrittle and fracture, resulting in reflection cracks in thepavement surface (see page 11 under Reflective Cracking).When selecting thicknesses for reclaimed pavements, athicker base with less strength should be preferred (seediscussion of Balanced Design on page 6). Today's morepowerful in-place pulverizing equipment has made the jobof obtaining thicker mixed-in-place layers much easier andmore reliable compared with equipment used years ago.

Mix Design

Designing the proper amount of water and cement for thestabilized base is not only important to obtain a good finalproduct, it also provides important information for qualitycontrol during construction. The PCA publication Soil-Cement Laboratory Handbook, EB052, providescomprehensive information on testing procedures for deter-mining the appropriate cement content, water content andcompaction requirements for cement-stabilized materials.Research has shown that cement-stabilized materials havebetter strength and performance when they are wellcompacted, so determining final compaction density isfundamental to the design procedure.

Compaction density is determined through the ASTMStandard Test Method for Moisture-Density Relations of Soil-Cement Mixtures (ASTM D558). The test procedure uses thestandard compaction effort similar to ASTM D698 (StandardProctor Test) for soils. The ASTM D558 test method is acommon (as well as inexpensive) procedure for mostconstruction testing labs. The test can be performed in either the laboratory or the field, and determines themaximum dry density (unit weight) for the FDR mix, and theinfluence of moisture content on obtaining that density.Figure 2.1 shows a typical compaction curve from the ASTMD558 test method. If the mix is too dry, there is not enoughmoisture available to lubricate the particles into a denserformation. If the mix is too wet, the excess moisture pushesthe particles apart. The moisture content where maximumdensity is selected for mix design and field quality control iscalled the “optimum moisture content.”

The amount of water in the mix is called the water content,and is defined as the weight of water in the mix (expressedas a percentage of the dry material).

water content, w (%) =weight of water in mix

X 100weight of oven-dry material

The amount of cement in the mix is expressed similarly:

cement content, c (%) =weight of cement in mix

X 100weight of oven-dry material

The amount of water and cement required in the mix willdepend upon the project specified strength and gradation ofthe final blend obtained from pulverizing the asphalt duringconstruction and mixing it with the base material. Typicalspecifications for pulverizing call for a minimum of 100%passing the 3-inch (75 mm) sieve, 95% passing the 2-inch (50 mm) sieve, and 55% passing the No. 4 (4.75 mm) sieve.If the blend contains more fine-grained soil, then morecement and water will be required because of the largersurface area of the finer particles.

The next step is to conduct a moisture-density test to determine the moisture content for molding the FDRspecimens for compressive strength testing. Since the exact cement content is not known at this stage of thedesign, an assumed cement content can be chosen inconducting the test. Table 1 in PCA publication Soil-CementLaboratory Handbook, may be used to estimate a cement

5% 7% 9% 11% 13% 15% 17%

125

120

115

110

105

100

Moisture Content

Dry

Den

sity

(lb

/cf)

ASTM D558

Maximum Dry Density

Optimum Moisture Content

Moisture/Density Relationship

Figure 2.1 Determining the Maximum Dry Density and OptimumMoisture Content (ASTM D558).

100 lb/cf = 1600 kg/cm

tional cracks to reflect through the pavement surface.The objective is to have a “balanced design,” whereenough cement is used so that the resulting stabilizedbase is strong, durable, and relatively impermeable, butnot so strong that it results in other types of distress inthe pavement.

Aggregate Adjustment

In some cases FDR is the preferred solution, but theexisting asphalt and base layers do not provide thedesired amount of aggregate for the new base. This can happen when the original pavement structure was under-designed, or traffic conditions have changedover the years, and a substantially heavier pavement is required.

In this situation an “aggregate adjustment” can bemade, where additional aggregate is placed on the pavement surface in a thin lift, and is then blended intothe base during the reclamation process. A picture of this process is shown in Figure 2.2.

Moisture Sensitivity

A new test procedure that shows a great deal of promise for future implementation is the Tube Suction Test. This test helps to identify base materials that may beparticularly sensitive to moisture degradation in the field,


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content for the moisture-density test. Cement contentswithin a range of one or two percent will notsignificantly influence theresults. However, once theexact cement content is established, a moisture-density test should beconducted with theestablished cement content in order to determine thecontrol factors for fieldconstruction.

Using the optimum moisturecontent from the initial mois-ture-density test, a series ofFDR specimens are prepared atdifferent cement contents to determine compressivestrength. Typically three cement contents are chosen (forexample, 3%, 5%, and 7%). It is recommended that a minimum of two specimens be prepared for each cementcontent. These specimens are moist-cured for 7 days, andthen tested for unconfined compressive strength accordingto ASTM Standard Test Method for Compressive Strengthof Molded Soil-Cement Cylinders (ASTM D1633). This willgive a range of strength results in which to determine therequired cement content.

Balanced Design

The stabilized base must be strong enough to provideadequate pavement support for the current and futuretraffic loading conditions. In addition, the stabilized baseneeds to remain hard and durable and be able to resist thevolume changes or hydraulic pressures caused by freezing-and-thawing and moisture changes that could graduallybreak down the cementitious bonds.

In general, a cement content that will provide a 7-dayunconfined compressive strength between 300-psi (2.1MPa) and 400-psi (2.8 MPa) is satisfactory for most FDRapplications. Higher strengths may be required if it is determined that the base materials are moisture sensitive,or that special conditions exist that warrant more strength.The main reason for limiting the strength is to keep thecement-stabilized base from becoming too brittle.Experience has shown that high strengths can cause addi-

Figure 2.2 Placing additional aggregate for inclusion in the FDR process.

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Chapter 2 Design

Figure 2.3 Tube Suction Tests measures the movement of water incement-stabilized material.

and to determine the correct amount of cement to use for stabilization.

The concept behind the Tube Suction Test is to measure themovement of water in a sample of cement-stabilized mate-rial. The test results can be evaluated to make sure thatenough cement is used to “choke off” the permeability and capillarity of the specimen.

PCA currently recommends the use of the Tube SuctionTest when working with materials that may be moisturesensitive, or when the presence of water may beespecially detrimental (such as in areas with deep frostpenetration). (Figure 2.3) More information on the TubeSuction Test can be found on PCA's Web site:www.cement.org/pavements.

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3 Construction

The construction process forfull-depth reclamation isstraightforward. It requiresthe following equipment:

• pulverizer/mixer

• grader

• cement spreader

• water truck

• roller

Pulverizing

The process begins bypulverizing the existing asphalt pavement (Figures 3.1 and 3.2).As discussed earlier, the depth of pulverizing should be more than the thickness of the existing asphalt. Modern equip-ment can pulverize to depths exceeding 18 inches (450 mm),but the difficulty lies with getting compaction deeper than 12 inches (300 mm). If the depth of pulverization exceeds 12 inches (300 mm), then the material should be windrowedand compacted in two lifts after treatment.

Pulverization can occur safely in urban areas with curb andgutter, manholes, and valve covers. The manholes, valvecovers, and other buried obstructions are removed below thedepth of the pulverization. Wooden or steel plates are usedto cover and protect the structures during the processingoperation. More than one pass of the pulverizing equipmentmay be necessary to achieve the required gradation.

Grading, Shaping, and Widening

Once the existing roadway has been pulverized and blendedtogether, the material is graded to the desired elevation andshape (Figure 3.3). When working between curb and gutter,

there may be a need to remove some of the pulverizedmaterial and haul it away in order to leave room for thepavement surface layer.

When the reclaimed road is being graded, it is an ideal time tomake improvements to the road crown, grade, drainage, andsuperelevation, because after stabilization the improvements

Figure 3.1 Inside a reclaimer.

Figure 3.2 Pulverizing a failed asphalt pavement.

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will be permanent. It is also an excellent time to perform roadwidening. Stabilizing the entire roadway creates uniformity ofthe pavement base that greatly reduces maintenancecompared to roads that are widened without being reclaimed.

Often following grading and shaping, the pulverized mate-rial will be compacted to accommodate traffic duringconstruction and improve uniformity for subsequent cementplacement and mixing operations.

Cement Placement

Cement is usually spread in a controlled manner by spreadertrucks that are designed for this operation. Placing thecement in an uncontrolled manner by blowing underpressure should be avoided.

Cement is most commonly applied dry (Figure 3.4), but canalso be applied in a slurry form (Figure 3.5). Most specificationscall for the application of cement in terms of weight per area(e.g., pounds of cement per square yard (kilograms of cementper square meter)). The most important time for dust control iswhen cement impacts the ground. Special enclosures can beused to minimize the amount of dust when cement is applied(Figure 3.6). Except for very windy days, dust should not be aproblem once the cement is on the ground. With a slurry appli-cation, it is important that the slurry be dispersed uniformlyover the placement area so that it will not pool or run off inany manner.

Chapter 3 Construcction

Figure 3.3 Grading and shaping.

Figure 3.6 Enclosure for dry cement application.

Figure 3.4 Placing cement dry.

Figure 3.5 Placing cement in slurry form.


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Mixing

Mixing is performed by the reclaimer/mixer, either byinjecting the proper amount of moisture into the mixingchamber (Figure 3.7), or by placing water on the ground with a water truck in a separate operation. In either case,obtaining the correct amount of moisture is very important in achieving the target compaction.

Curing

Proper curing is very important to the quality of the finalproduct. If the base is allowed to dry, it will develop cracks,and the continued gain in strength over time will be compromised. The cement-treated base must be kept moista minimum of 7 days following compaction. Proper curingcan be achieved by continuous water spraying or applicationof an approved sealing compound or membrane. If the roadwill have an asphalt surface, a bituminous prime-coat can beapplied at any time, as this will act as a curing membrane.

Surfacing

The cement-treated base (CTB) that results from the FDRprocess can have any type of pavement surfacing (e.g., chipseal surface treatment, hot mixed asphalt, or concrete). Thesurfacing can be applied as soon as the CTB is stable (doesnot rut or shove) under construction traffic. The timerequired for this can range from 4 to 48 hours.

Traffic can be placed on the CTB in the same time frame, aslong as repeated applications of heavy trucks are not involved.In many cases with low-volume roads, traffic is allowed to runon the compacted base until the project is ready for surfacing.For conditions where heavy truck traffic is involved, up to 7 days may be required to make sure the base has gainedsufficient strength for a high volume of heavy trucks.

Field Quality Control

Field quality control procedures are similar to those used forstandard cement-treated base. A thorough discussion onfield inspection and testing procedures can be found in PCApublication Soil-Cement Inspectors Manual, PA050.

Traffic Control

The FDR process can be performed under traffic (Figure 3.9and Figure 3.10). With low-volume roads, traffic is usuallyallowed on one side of the road while construction occurson the other. Traffic is controlled with flagmen. With someprojects, vehicles are allowed on the finished CTB prior tosurfacing. On other projects, traffic will not return to thelane until surfacing is finished.

For projects with higher traffic volumes, a surface treatmentover the new CTB acts as an excellent curing membrane and allows traffic to travel easily until the roadway is readyfor surfacing.

Figure 3.7 Water being injected during mixing operation.

Figure 3.8 Compaction and final grading.

Compaction and Final Grading

After the materials are well mixed, it is time for compactionand final grading (Figure 3.8). Smooth-wheeled vibratingrollers, or tamping rollers can be used to provide initialcompaction, with smooth-wheeled or pneumatic-tire rollersused to complete the operation. Once the cement is mixedwith water and the pulverized base material, the maximumtime allowed for compaction is 2 hours.

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Reflective Cracking

Cement-treated materials will shrink naturally while curing.With properly designed pavements, and good constructionprocedures, the resulting cracks in the base will notsignificantly affect pavement performance. In some caseslarger cracks in the base layer can result in stress concentra-tions, and the cracks may reflect from the base into thesurface. This does not normally affect pavement roughness,but may influence the overall appearance of the pavement.

Usually proper construction procedures, crack minimizationstrategies, and maintenance sealing, if necessary, can elimi-nate requirements for significant maintenance due to reflec-

tive cracking. Newer techniques, such as micro-cracking orusing a stress absorbing inter-layer, have been verysuccessful. A well designed and properly maintainedcement-treated base will normally outlast several asphaltoverlays, providing decades of low maintenance service.

More information on control of reflective cracking incement-treated bases can be found in the following PCA documents:

Reflective Cracking in Cement-Stabilized Pavements, IS537

Minimizing Cracking in Cement-Treated Materials forImproved Performance, RD123.

Chapter 3 Construcction

Figure 3.9 Traffic being allowed on completed FDR base prior tosurfacing while processing operation proceeds in adjacent lane.

Figure 3.10 Traffic control in an urban area.


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4 Suggested Construction Specification for Full-Depth Reclamation

1. GENERAL

1.1 Description. Full-depth reclamation (FDR) withcement, shall consist of pulverizing and mixing existingasphalt pavement and base course material with portlandcement, soil and water to produce a dense, hard, cement-treated base. It shall be proportioned, mixed, placed,compacted, and cured in accordance with this specification,and shall conform to the lines, grades, thicknesses, andtypical cross sections shown in the plan.

1.2 Caveat. This specification is intended to serve as aguide to format and content for normal FDR construction.Most projects have special features or requirements thatshould be incorporated in the project documents.

2. MATERIALS

2.1 Recycled Asphalt Pavement (RAP) and BaseMaterial. Shall consist of the existing asphalt pavement,existing base course material and/or subgrade material. Thebase course and subgrade material shall not contain roots,topsoil, or any material deleterious to its reaction withcement. The particle distribution of the processed materialshall be such that 100% passes a 3-inch (75 mm) sieve, atleast 95% passes a 2-inch (50 mm) sieve, and at least 55%passes a No. 4 (4.75 mm) sieve.

2.2 Portland Cement. Shall comply with the latest speci-fications for portland cement (ASTM C 150, ASTM C 1157,or AASHTO M 85) or blended hydraulic cements (ASTM C 595, ASTM C 1157, or AASHTO M 240).

2.3 Water. Shall be free from substances deleterious to thehardening of the cement-treated material.

2.4 Pozzolans. If used, pozzolans including fly ash, slag,and silica fume shall comply with the appropriate specifications(ASTM C 618, AASHTO M 295 for fly ash; ASTM C 989,AASHTO M 302 for slag; and ASTM C 1240 for silica fume).

3. EQUIPMENT

3.1 Description. FDR may be constructed with any machineor combination of machines or equipment that will produce asatisfactory product meeting the requirements for pulverization,cement and water application, mixing, compacting, finishing,and curing as provided in this specification.

3.2 Mixing Methods. Mixing shall be accomplished inplace, using single-shaft or multiple-shaft mixers. Agriculturaldisks or motor graders are not acceptable mixing equipment.

3.3 Cement Proportioning. Cement can be added in adry or slurry form. If applied in slurry form, the slurry mixerand truck shall be capable of completely dispersing thecement in the water to produce a uniform slurry, and shallcontinuously agitate the slurry once mixed.

3.4 Application of Water. Water may be applied through themixer or with water trucks equipped with pressure-spray bars.

3.5 Compaction. The processed material shall becompacted with one or a combination of the following:tamping or grid roller, pneumatic-tire roller, steel-wheel roller,vibratory roller, or vibrating-plate compactor.

4. CONSTRUCTION REQUIREMENTS

4.1 General

4.1.1 Preparation of Subgrade. Before processing begins,the area to be processed shall be graded and shaped to linesand grades as shown in the plans or as directed by theengineer. During this process, any unsuitable soil or materialshall be removed and replaced with acceptable material. Anymanholes, valve covers, or other buried structures shall beprotected from damage prior to processing. The subgrade shallbe firm and able to support, without yielding or subsequentsettlement, the construction equipment and the compaction ofthe FDR material. Soft or yielding subgrade shall be correctedand made stable before construction proceeds.

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4.1.2 Mixing and Placing. FDR processing shall notcommence when the soil aggregate or subgrade is frozen, orwhen the air temperature is below 40°F (4°C). Moisture inthe base course material at the time of cement applicationshall not exceed the quantity that will permit a uniform andintimate mixture of the pulverized asphalt, base material andcement during mixing operations, and shall be within 2% ofthe optimum moisture content for the processed material atstart of compaction.

The operation of cement application, mixing, spreading,compacting, and finishing shall be continuous and completedwithin 2 hours from the start of mixing. Any processed mate-rial that has not been compacted and finished shall not beleft undisturbed for longer than 30 minutes.

4.2 Pulverization/Mixing

4.2.1 Preparation. The surface of the pavement prior tomixing shall be at an elevation so that, when mixed withcement and water and recompacted to the required density,the final elevation will be as shown in the plans or asdirected by the engineer. The material in place and surfaceconditions shall be approved by the engineer before the nextphase of construction is begun.

4.2.2 Scarifying. Before cement is applied, initial pulveriza-tion or scarification may be required to the full depth ofmixing. Scarification or pre-pulverization is a requirement forthe following conditions:

1) When the processed material is more than 3% above orbelow optimum moisture content. When the material isbelow optimum moisture content, water shall be added.The pre-pulverized material shall be sealed and properlydrained at the end of the day or if rain is expected.

2) For slurry application of cement, initial scarification shallbe done to provide a method to uniformly distribute theslurry over the processed material without excessiverunoff or ponding.

4.2.3 Application of Cement. The specified quantity ofcement shall be applied uniformly in a manner thatminimizes dust and is satisfactory to the engineer. If cementis applied as a slurry, the time from first contact of cementwith water to application on the soil shall not exceed 60minutes. The time from cement placement on the soil tostart of mixing shall not exceed 30 minutes.

4.2.4 Mixing. Mixing shall begin as soon as possible afterthe cement has been spread and shall continue until auniform mixture is produced. The mixed material shall meetthe following gradation conditions:

1) The final mixture (bituminous surface, granular base, andsubgrade soil) shall be pulverized such that 100% passesthe 3-inch (75 mm) sieve, at least 95% passes the 2-in.(50 mm) sieve, and at least 55% passes the No. 4 (4.75mm) sieve. No more than 50% of the final mixed materialshall be made of the existing bituminous material unlessapproved by the engineer and included in a mixturedesign. Additional material can be added to the top orfrom the subgrade to improve the mixture gradation, aslong as this material was included in the mixture design.

2) The final pulverization test shall be made at theconclusion of mixing operations. Mixing shall becontinued until the product is uniform in color, meetsgradation requirements, and is at the required moisturecontent throughout. The entire operation of cementspreading, water application, and mixing shall result in auniform pulverized asphalt, soil, cement, and watermixture for the full design depth and width.

4.3 Compaction. The processed material shall beuniformly compacted to a minimum of 98% of maximumdensity based on a moving average of five consecutive testswith no individual test below 96%. Field density ofcompacted material can be determined by nuclear method inthe direct transmission mode (ASTM D 2922, AASHTO T310), sand cone method (ASTM D 1556, AASHTO T 191), orrubber balloon method (ASTM D 2167). Optimum moistureand maximum density shall be determined prior to start ofconstruction and also in the field during construction by amoisture-density test (ASTM D 558 or AASHTO T 134).

At the start of compaction, the moisture content shall bewithin 2% of the specified optimum moisture. No sectionshall be left undisturbed for longer than 30 minutes duringcompaction operations. All compaction operations shall becompleted within 2 hours from start of mixing.

4.4 Finishing. As compaction nears completion, thesurface of the FDR material shall be shaped to the specifiedlines, grades, and cross sections. If necessary or as requiredby the engineer, the surface shall be lightly scarified orbroom-dragged to remove imprints left by equipment or toprevent compaction planes. Compaction shall then becontinued until uniform and adequate density is obtained.During the finishing process the surface shall be kept moistby means of water spray devices that will not erode thesurface. Compaction and finishing shall be done in such amanner as to produce a dense surface free of compactionplanes, cracks, ridges, or loose material. All finishing opera-tions shall be completed within 4 hours from start of mixing.

Chapter 4 Suggested Construction Specification for Full-Depth Reclamation


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4.5 Curing. Finished portions of the FDR base that are trav-eled on by equipment used in constructing an adjoining sectionshall be protected in such a manner as to prevent equipmentfrom marring or damaging completed work.

After completion of final finishing, the surface shall be cured by application of a bituminous or other approved sealingmembrane, or by being kept continuously moist for a periodof 7 days with a water spray that will not erode the surface ofthe FDR base. If curing material is used, it shall be applied assoon as possible, but not later than 24 hours after completingfinishing operations. The surface shall be kept continuouslymoist prior to application of curing material.

For bituminous curing material, the FDR base surface shall bedense, free of all loose and extraneous materials, and shallcontain sufficient moisture to prevent excessive penetrationof the bituminous material. The bituminous material shall beuniformly applied to the surface of the completed cement-treated material. The exact rate and temperature of applica-tion for complete coverage, without undue runoff, shall bespecified by the engineer.

Should it be necessary for construction equipment or othertraffic to use the bituminous-covered surface before the bituminous material has dried sufficiently to prevent pickup,sufficient sand cover shall be applied before such use.

Sufficient protection from freezing shall be given thecement-treated material for 7 days after its construction oras approved by the engineer.

4.6 Traffic. Completed portions of FDR base can beopened immediately to low-speed local traffic and toconstruction equipment, provided the curing material ormoist curing operations are not impaired, and provided theFDR base is sufficiently stable to withstand marring orpermanent deformation. The section can be opened up to alltraffic after the FDR base has received a curing compound orsubsequent surface and is sufficiently stable to withstandmarring or permanent deformation. If continuous moistcuring is employed in lieu of a curing compound orsubsequent surfacing within 7 days, the FDR base can beopened to all traffic after the 7-day moist curing period,provided the FDR base has hardened sufficiently to preventmarring or permanent deformation.

4.7 Surfacing. Subsequent pavement layers (asphalt, chip-seal, or concrete) can be placed any time after finishing, aslong as the soil-cement is sufficiently stable to support therequired construction equipment without marring or perma-nent distortion of the surface.

4.8 Maintenance. The contractor shall maintain thecement-treated material in good condition until all work iscompleted and accepted. Such maintenance shall be done bythe contractor at his own expense.

Maintenance shall include immediate repairs of any defectsthat may occur. If it is necessary to replace any processed material, the replacement shall be for the full depth, withvertical cuts, using either cement-treated material orconcrete. No skin patches will be permitted.

5. INSPECTION AND TESTING

5.1 Description. The engineer, with the assistance andcooperation of the contractor, shall make such inspections and tests as deemed necessary to ensure the conformance of the work to the contract documents. These inspections and tests may include, but shall not be limited to:

1) Obtaining test samples of the cement-treated material andits individual components at all stages of processing andafter completion.

2) Observing the operation of all equipment used on thework. Only those materials, machines, and methodsmeeting the requirements of the contract documents shallbe used unless otherwise approved by the engineer.

All testing of processed material or its individual components,unless otherwise provided specifically in the contractdocuments, shall be in accordance with the latest applicableASTM or AASHTO specifications in effect as of the date ofadvertisement for bids on the project.

6. MEASUREMENT AND PAYMENT

6.1 Measurement. This work will be measured:

1) In square yards (meters) of completed and accepted FDRbase course as determined by the specified lines, grades,and cross sections shown on the plans.

2) In tons (tonnes) or cwt of cement incorporated into theFDR base course in accordance with the instructions of theengineer.

6.2 Payment. This work will be paid for at the contract unitprice per square yard (meter) of FDR base course and at thecontract unit price per ton (tonne) or cwt of cement furnished,multiplied by the quantities obtained in accordance withSection 6.1. Such payment shall constitute full reimbursementfor all work necessary to complete the FDR base course,including watering, curing, inspection and testing assistance,and all other incidental operations.

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Chapter

An organization of cement companies to improve

and extend the uses of portland cement and concrete

through market development, engineering, research,

education and public affairs work. EB234.01

Documents

PCA EB234 Guide to Full-Depth Reclamation (FDR) With Cement